Coal acid esters as synthetic lubricants



Patented Sept. 25, 1951 UNITED STATES PATENT OFFICE COAL ACID ESTERS AS SYNTHETIC LUBRICANTS Charles W. Montgomery and William I. Gilbert, Oakmont, and Robert E. Kline, Penn Township, Allegheny County, Pa., asslgnors to Gulf Research a Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application May 26, 1947,

. Serial No. 750,644 I gregation of properties adapting them for use for a wide variety of purposes, and furthermore petroleum lubricants are relatively cheap to prepare. Various synthetically derived lubricants have been suggested from time to time but they have not acquired widespread use, either because of their suitability for only certain specific uses or because of the fact that they are costly to pre- It is an object of this invention, therefore, to provide synthetic lubricants which may successfully be aplied to uses for which petroleum lubricants have heretofore been employed.

It is a further object of this invention to provide a synthetic lubricant that can be easily and cheaply prepared.

These and other objects are attained by the present invention wherein we provide as a lubricant for reducing the coeflicient of friction between metal surfaces moving in contact with and relative to each other a film of a substantially neutral ester of a monohydric alcohol and the mixture of acids obtained by the oxidation with gaseous oxygen of an acqueous alkaline slurry of a finely divided carbonaceous material selected to synthetic lubricants charge.

sisting of coal and coke obtained by the carbonization of coal at temperatures below 700 C. Suitable coals comprise anthracite, bituminous, sub-bituminous, lignite and other low grade coals. Suitable cokes are those produced by the carbonization of a coal at a temperature below 700 C., in a manner known to the art. If the cakes are produced at temperatures in excess of 700 (7., they become graphitic and unsuitable for the production of coal acids in a satisfactory yield.

The following is an example of the preparation of the coal acids.

Finely ground bituminous coal, alkali, such as sodium hydroxide, and water are mixed in a nickel-lined autoclave equipped with a turbomixer and with means for heating and cooling the The amount of alkali used is in excess of that required completely to neutralize all of the coal acids formed in the oxidation process.

, By way of example, the proportions of the ingredients may be 15 pounds of coal, 15 gallons of water and 45 pounds of caustic soda. The charge is heated and then oxygen is bubbled therethrough. The temperature of the charge is maintained from 200 to 300 C. at a total pressure of from 500 to 1200 pounds per square inch. The reaction is exothermic and the temperature is maintained within the limits stated by cooling, such as by passing water through an internal cooling coil in the autoclave. The oxidation is continued until all of the carbonaceous material of the coal passes into solution and usually requires between 2 and 3 hours. Half of the carbon from the group consisting of coal and coke nomically and therefore do not suffer the high cost disadvantages of many prior art synthetic lubricants.

As has been stated, the acids used in the preparation of our synthetic lubricants are obtained by the oxidation with gaseous oxygen of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group conof the coal is oxidized to organic acids and the remainder to carbon dioxide. At the completion of the oxidation the charge is cooled to about C. and is discharged from the autoclave. The ash of the coal, which is largely unattacked, is removed by filtering through a filter press.

The filtered product is an alkaline solution containing the sodium salts of the organic acids obtained by the oxidation of the coal. Enough sulfuric acid is added to this solution to liberate the free acids. Any insoluble material appearing after acidification with sulfuric acid is removed by filtering. The free coal acids obtained are water-soluble and may conveniently be obtained from their solution in water by extraction with a suitable water-immiscible organic solvent. Methyl ethyl ketone is a suitable solvent, since in the presence of the sodium sulfate produced by the acidification with sulfuric acid, methyl ethyl ketone is water-immiscible. The extract phase may then be transferred to a still for recovery of the bulk of the solvent, and the prod- 3 not remaining in the still may then be fed to a vacuum rotary drier for removal of the remainder of the solvent. For convenience in subsequent handling, the dried product may be 4 atemperatmeof150'to200C..andarethen filtered. when this treatment was applied to the mrmalbutylesters,anincreaseintheviscosity index from 76 to 92 was obtained.

ground to a fine powder in a pebble mill. 5 Representative properties of some of the aters The product obtained appears to be a mixture of this invention are shown in the following of aromatic acids. This mixture is a free-flowing table:

vs. Vis. m mall 11 r '0 1! ssu r ssuu v1 Pa,

M or 1001:. znrr. 'r.

n-Butyl (crude) m an :71... 1M a 1am I... am 1m 1s n-Butyl (treatedfi... great: an :71... 1.10 at lav/m 1'.-- in, no sun 92 n-Octyl (crude) greet: M am--- 1.0m at IIIQ I.-- l, 654 117 Hi 0 n-Octyl (treated) milieu--. ism-sewer I, m 94 0 n-Lauryl (crude).. Mull.-- muse-pr I--. 1,218 116 116 +5 n-Lauryl (treated) greater-m--- mat fi'll 1,37 l!) 116 +80 Trestedwith fulierseanhandlmamdhdmedinthe xeeedingplagnph.

yellow powder which is hygroscopic and substantially completely soluble in water. The average molecular weight of the acids is 250 and the average equivalent weight is 80. According y. the average number of carboxyl groups per molecule is somewhat more than 3. The exact nature of the acids is unknown, but they are believed to contain triand tetra-carboxylic benzene acids, as well as acids having a more complex nucleus than the benzene ring. Y

In order to obtain the synthetic lubricants of our invention. the coal acids as obtained above are esterifled with a monohydric alcohol to produce substantially neutral esters. Esteriflcation may conveniently be carried out by refluxing 6 moles of the alcohol with 1 mole of the coal acids for several hours while continuously adding small amounts of anhydrous hydrogen chloride as a catalyst. Water is continuously removed from the reaction vessel until the theoretical amount oi separated water indicates that reaction is complete. At this point any excess of the alcohol is allowed to distill out of the reaction vessel. Other methods of esteriflcation may be employed, as will be understood in the art.

A wide variety of monohydric alcohols may be employed for the esterification. For example, the alkanols, particularly the straight chain alkanols containing up to 20 carbon atoms. such as methyl, ethyl, propyl, butyl, amyl, hexyl. octyl, decyl, lauryl, myristyl, palmityl and eicosyl alcohols yield excellent products. Branched chain alkanols such as isopropyl alcohol, Z-ethyl-hexyl alcohol, and the like may also be employed. Other monohydric alcohols which may be employed are the unsaturated aliphatic alcohols such as allyl alcohol, crotonyl alcohol, oleyl alcohol and the like. Alicyclic and aromatic monohydric acohols such as cyclohexanol and benayl alcohol are also suitable. Mixtures of monohydric alcohols may also be employed, particularly the mixture of alcohols obtained by the reduction of coconut oil fatty acids and known commercially as Lorol, the mixture of higher molecular weight alcohols obtained as a byproduct in the synthesis of methanol .from carbon monoxide and hydrogen, as well as the mixture of alcohols obtained as byproducts in the synthcsh of hydrocarbons from carbon monoxide and hydrogen. A preferred sub-group of monohydric alcohols comprises the straight chain aliphatic alcohols containing from 4 to 12 carbon atoms.

If desired, the esters obtained as indicated above may be treated with lime and an absorbent, such as fullers earth, to improve their 'lheestersofthecoalacidsobtainedasdescribedintheforegdmdisclosu'representa number of properflu making them eminently mitableaslubrlcants. Theyhave ahigh viscosity index. The high initial boiling points and extremeb low'vapor premures of the esters, even at elevated temperabnes, render any loss of these lubricants by vaporization under service condiflom extremely remote. As a matter of faet,theestersofcoalaeidscannotbedistllledln appreciable amormts by ordinary distillation techniques and can onlybe partially fractionated by molecular distillation. The lubricants of our invention are very stable and thus may advantageously be used under conditions where oxidation and sludge formation of petroleum lubricants are likely to be encountered as, for example, when used as crank case lubricants for gasoline and diesel engines. Purthermore'the estersmaybeusedinlieuoimineral oil for the compoundirm of lubricating greases by the compormding procednru known in the art. The esters also have excellent oiliness" and pressurecarrying properties. For example, the iauryl ester of the coal aekb was tested in the Pale: Lubrbant Testing llachine, and, for comparison, a good grade of a paramnic petmlemn lubricating oilwassubiectedtothesametest. Thefollowing showthemarkcdimprovement in wear and our lubricants:

b has... zimi'fis s g mum-scans H03 momma LII ltolii snowman 'lhel'alexhlbricanttutlngmachineisessem' the pin and V-blocks are completely immersed in properties. For example, in one such treatment the esters are stirred with 4 per cent by weight of theoll. 'lhepinisstartedmtatingatZQORPJl. andtheratchetwheelisturnedupuntilaforce oIMpmmdonthebearirxsurIaceisindicatedon a suitable gauge. Under these conditiom, a break-innmof yhourismsde. After-the hour break-in period, the ratchet wheel is fur.-

fuller'searthandipercentbyweightoflimeat 1! the:-

up the bearing load is 100 aooaooc pounds and the position of an index tooth of the ratchet wheel, relative to any fixed point near the periphery of the wheel, is noted. The

test is continued for three more hours under these amount of wear that has occurred. The results of the test are reported as the "number of teeth, e. g. 5 teeth," teeth," etc.

The Falex seizure test is run in the same machine, using the same amount of oil to surround the V-blocks and rotating pin as is used for the Falex wear test. Likewise the same speed of 290 R. P. M. is employed for the rotating pin. In the Falex seizure test a break-in period of ten minutes at a bearing load of 250 pounds is employed. At the end of the ten minutes break-in period at 250 pounds the bearing pressure is increased to 300 pounds and in regular 100 pound increments every three minutes thereafter until the pin seizes" or until a maximum load of 2500 pounds is achieved. The seize-point is characterized by a sudden large increase 01' torque which can be seen on a torque indicator which is operated in conjunction with the rotating pin. The test result is expressed as the bearing load at which seizure occurs.

Although we have disclosed the use of our lubricants in lieu of mineral oils, the esters herein disclosed may be added to mineral lubricating oils in a minor proportion, say from about 0.1 to 20 per cent by weight, suflicient to confer one or more improved properties, such as retarding of rusting and improved oiliness and pressure-carrying properties, on the lubricating composition. Thus, for example, the addition of 20 per cent by weight of the lauryl ester disclosed herein to a. mineral lubricating oil confers enhanced oiliness and pressure-carrying properties. When 0.1 per cent by weight of the lauryl ester was added to a mineral lubricating oil and the composition subjected to the ASTM corrosion test, designated ASTM D-665.-44T, in the presence of distilled water, the composition passed the test, that is, there was no rust after 48 hours. The same mineral lubricating oil without the addition of the lauryl ester permitted heavy rusting after about 4 hours. We consider such improved mineral lubricating oil compositions containing the monohydric alcohol esters of the coal acids to be a part of our invention.

An outstanding advantage of the lubricants of our invention is that lubricants having properties desired for a specific app ication may be simply and economically prepared merely by varying the monohydric alcohol used for esterification oi the coal acids. For example, the normal butyl esters of the coal acids make an excellent lubricant for transmissions, difierentials and other gear type mechanisms where high viscosity and high load carrying capacity are required; whereas the lauryl esters oi. the coal acids make an excellent lubricant for internal combustion engines, such as gasoline and diesel engines.

What we claim is:

l. A process of reducing the coeilicient of friction between metal surfaces moving in contact with and relative to each other which comprises lubricating said surfaces by a film of a substanthe mixture of aromatic acids obtained by the oxidation with gaseous oxygen at a temperature from about 200 to about 300 C. and at a pressure from about 500 to about 1200 pounds per square inch of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting of coal and coke obtained by the carbonization of coal at temperatures below 700 0., the acidification of the resulting alkaline solution to liberate said acids and the extraction of said acids with an organic water-immiscible solvent which will remove the acids.

2. The process of claim 1, wherein the monohydric alcohol is an alkanol containing up to 20 carbon atoms.

3. The process of claim 1, wherein the monohydric alcohol is a straight chain alkanol containing from 4 to 12 carbon atoms.

4. The process of claim 1, wherein the monohydric alcohol is butyl alcohol.

5. The process of claim 1, wherein the monohydric alcohol is octyl alcohol.

6. The process of claim 1, wherein the monohydric alcohol is lauryl alcohol.

7. The process of claim 1, wherein the carbonaceous material is finely divided bituminous coal.

8. A process for reducing the coefllcient of friction between metal surfaces moving in contact with and relative to each other which comprises lubricating said surfaces by a film of a lubricant comprising a major amount of a mineral lubricating oil and a minor amount suflicient to retard rusting of a substantially neutral ester of a monohydric alcohol and the mixture of aromatic acids obtained by the oxidation with gaseous oxygen at a temperature from about 200 to about 300 C. and at a pressure from about 500 to about 1200 pounds per square inch of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group con sisting of coal and coke obtained by the carbonization of coal at temperatures below 700 C., the acidification oi the resulting alkaline solution to liberate said acids and the extraction of said.

acids with an organic water-immiscible solvent which will remove the acids.

9. The process of claim 8, wherein the ester is added in an amount 01' from 0.1 to 20 per cent by weight 01' the mineral lubricating oil.

10. A lubricant composition comprising a major amount of a mineral lubricating oil and a minor amount, at least suilicient to retard rusting, of a substantially neutral ester of a monohydric alcohol and the mixture of aromatic acids obtained by the oxidation with gaseous oxygen at a temperature from about 200 to about 300 C. and at a pressure from about 500 to about 1200 pounds per square inch of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting of coal and coke obtained by the carbonization of coal at temperatures below (00 C., the acidification of the resulting alkaline solution to liberate said acids and the extraction of said acids with an organic water-immiscible solvent which will remove the acids.

11. The composition of claim 10, wherein the carbonaceous material is finely divided bituminous coal.

12. The composition oi. claim 10, wherein the monohydric alcohol is an alkanol containing up tially neutral ester of a monohydric alcohol and to 20 carbon atoms aoeapoe 13. The composition 01 claim 10, wherein the monohydric alcohol is a straight chain alkanol containing from 4 to 12 carbon atoms.

14. The composition of claim 10, wherein the monohydric alcohol is butyl alcohol.

15. The composition of claim 10, wherein the monohydric alcohol is octyl alcohol.

16. The composition of claim 10, wherein the monohydric alcohol is lauryl alcohol.

17. The composition of claim 10, wherein the ester is added in an amount of from 0.1 to 20 per cent by weight of the lubricating oil.

18. A lubricant composition comprising a ma-- jor amount of a mineral lubricating oil and from 0.1 to 20 per cent by weight on the oil of the substantially neutral ester of lauryl alcohol and the mixture of aromatic acids obtained by the oxida-- tion with gaseous oxygen at a temperature from about 200 to about 300 C; and at a pressure from about 500 to about 1200 pounds per square inch of an aqueous alkaline slurry of finely divided bituminous coal, the acidification of the resulting alkaline solution to liberate said acids and the extraction of said acids with an organic watier-immiscible solvent which will remove the acids.

19. A lubricant composition comprising a major amount of a mineral lubricating oil and a minor amount, sufllcient to retard rusting, oi the substantially neutral ester 01 lauryl alcohol and the mixture of aromatic acids obtained by the oxidationwith gaseous oxygen at a temperature from about 200 to about 300' C. and at a pressure from about 500 to 1200 pounds per square inch of an aqueous alkaline slurry of finely divided bituminous coal. the acidification or the resulting alkaline solution to liberate said acids and the extraction of said acids with an organic water-immiscible solvent which will remove the acids.

CHARLES W. MONTGOMERY. WILLIAM I. GILBERT. ROBERT E. KLINI.

REFERENCES CITED The following references are oi record in the file of this patent:

UNITED STATE 

1. A PROCESS OF REDUCING THE COEFFCIENT OF FRICTION BETWEEN METAL SURFACES MOVING IN CONTACT WITH AND RELATIVE TO EACH OTHER WHICH COMPRISES LUBRICATING SAID SURFACES BY A FILM OF A SUBSTANTIALLY NEUTRAL ESTER OF A MONOHYDRIC ALCOHOL AND THE MIXTURE OF AROMATIC ACIDS OBTAINED BY THE OXIDATION WITH GASEOUS OXYGEN AT A TEMPERATURE FROM ABOUT 200* TO ABOUT 300* C. POUNDS PER SURE FROM ABOUT 500 TO ABOUT 1200 POUNDS SQUARE INCH OF AN AQUEOUS ALKALINE SLURRY OF A FINELY DIVIDED CARBONACEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF COAL AND COKE OBTAINED BY THE CARBONIZATION OF COAL AT TEMPERATURES BELOW 700* C., THE ACIDIFICATION OF THE RESULTING ALKALINE SOLUTION TO LIBERATE SAID ACIDS AND THE EXTRACTION OF SAID ACIDS WITH AN ORGANIC WATER-IMMISCIBLE SOLVENT WHICH WILL REMOVE THE ACIDS.
 10. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A MINERAL LUBRICATING OIL AND A MINOR AMOUNT, AT LEAST SUFFICIENT TO RETARD RUSTING, OF A SUBSTANTIALLY NEUTRAL ESTER OF A MONOHYDRIC ALCOHOL AND THE MIXTURE OF AROMATIC ACIDS OBTAINED BY THE OXIDATION WITH GASEOUS OXYGEN AT A TEMPERATURE FROM ABOUT 500 TO ABOUT 300* C. AND AT A PRESSURE FROM ABOUT 500 TO ABOUT 1200 POUNDS PER SQUARE INCH OF AN AQUEOUS ALKALINE SLURRY OF A FINELY DIVIDED CARBONACEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF COAL AND COKE OBTAINED BY THE CARBONIZATION OF COAL AT TEMPERATURE BELOW 700* C., THE ACIDIFICATION OF THE RESULTING ALKALINE SOLUTION TO LIBERATE SAID ACIDS AND THE EXTRACTION OF SAID ACIDS WITH AN ORGANIC WATER-IMMISCIBLE SOLVENT WHICH WILL REMOVE THE ACIDS. 